In the field of semiconductors such as LEDs and power modules, higher degree of integration and power density are increasingly demanded, techniques of heat dissipation in the periphery of an integrated circuit are gaining greater importance as a factor determining such performance measures.
In particular, since organic materials used in implementation are difficult to conduct heat, the need for improved heat dissipation properties becomes more pronounced as the degree of integration increases.
Conventionally, silica and alumina have been used as materials with improved heat dissipation properties as mentioned above, in terms of price, stability of their quality, and their compatibility with resin.
However, with the aforementioned conventional materials, attempts have been made to improve performance by spheroidization, optimization of particle size distribution, and so on, yet there are limits on the improvement.
Therefore, there is an increasing demand for a new filling material obtained by changing the blank material itself.
Accordingly, AlN, MgO, BeO, and BN have newly gained increased attention as inorganic materials with high thermal (heat) conductivity.
Among others, BN is excellent in its insulating properties, environmental stability, and moisture absorption resistance, and has been studied as a most promising candidate.
However, BN particles are scaly, and have hexagonal crystal structure, which shows anisotropic, and thus unstable properties, leading to the problem of being unable to fully make use of potential properties of BN.
In addition, surfaces of BN particles involve a small number of functional groups and have poor adhesiveness to the base polymer material. Thus, a crack occurs in the interface between a BN particle and the polymer material, which causes separation of a copper foil from the polymer material easily at the interface with reduced strength in the presence of the BN particle. This results in another problem of causing exfoliation of the copper foil as a circuit during use, leading to conduction failure.
To date, many improvements have been made to BN particles in order to address the aforementioned difficulties.
For example, JPH1160216A (PTL 1) proposes a method of forming a polymer composite material such that a-axis of BN particles is aligned perpendicular to the heat dissipating route.
In addition, JP3461651B (PTL 2) proposes a method in which BN powder is formed of aggregates such that the particles are isotropic.
Moreover, JP201076955A (PTL 3) proposes a method of reducing the particle size of BN particles so as to obtain less anisotropic particles.
The aforementioned methods can indeed produce some degree of improving effects. However, they are not still sufficient in terms of heat dissipation properties and adhesiveness.